This invention relates generally to portable electric room air heaters and particularly to upright radiant heaters suitable for placement in a corner or any other location in a room while occupying a minimum amount of floor space. As will become apparent to those familiar with the art, aspects of this invention may be used with other types of heaters.
An upright or so-called xe2x80x9ctowerxe2x80x9d heater is relatively tall in relation to its horizontal area or xe2x80x9cfootprint.xe2x80x9d Examples are shown in U.S. Design Pat. No. 111,000, granted Aug. 23, 1938, to C. Knox et al., and U.S. Design Pat. No. 141,834 granted to W. E. Maxson, Jr. on Jul. 10, 1945. These may be contrasted to horizontal heaters that have a relatively low profile, such as shown in U.S. Pat. No. 3,175,550, issued to R. S. Knapp on Mar. 30, 1965, U.S. Pat. No. 3,059,090, granted to R. S. Waters on Oct. 16, 1962, and U.S. Pat. No. 3,610,882, issued to William A. Omohundra on Oct. 5, 1971.
One of the problems encountered in any portable heater is the creation of localized xe2x80x9chot spotsxe2x80x9d on or adjacent the heater. These are areas that get much hotter than adjacent areas. Hot spots are undesirable because they can present a fire hazard as well as cause discomfort to the user of a heater. Portable electric air heaters sold in the United States at this time must meet testing requirements of Underwriter""s Laboratories, Inc. when in actual service, so that the heaters do not present a risk of fire, electric shock or personal injury when operated continuously under abnormal conditions. With many heaters, such tests can only be passed successfully by the use of relatively expensive safety control devices.
An object of this invention is to provide a portable heater which is inherently designed to avoid the formation of hot spots and therefore, avoid the need for all but basic electrical safety devices.
Another object of the invention is to provide an efficient, upright radiant electric heating appliance which occupies minimal floor space, is easy to operate, and which is capable of heating a room relatively rapidly.
Another object is to provide a thermostatically-controlled room air heater with accurate on-and-off cycling to maintain or increase to desired room temperatures. Ancillary thereto is an object of minimizing, simplifying and reducing cost of the structure for controlling such a thermostat.
Another object of the invention is the provision of such a heater which has exterior housing portions which are relatively cool to the touch, thereby allowing such portions to be produced from thermoplastic molded materials that may readily be manufactured to various different shapes. This enables designers of heaters to design heaters of various aesthetically pleasing designs that may be produced at lower costs than similar heaters which have all metal housings.
An upright radiant electric heating appliance in accordance with this invention has a reflector assembly that includes radiant heat reflective side panels which lie in vertical planes that intersect one another at an included angle of between 90 and 180 degrees, a vertically-extending heating element assembly located near the rear of the reflector assembly that radiates heat energy throughout substantially 360 degrees in a horizontal direction, and a circular open grill at the front of the reflector assembly. Heat energy is directly radiated by the heating element assembly through the open grill or reflected by the reflective side panels through the open grill.
In a preferred embodiment, the heating element assembly is preferably spaced on the order of eight inches or more from the open grill and each reflective side panel is similarly spaced from the opposite side of the open grill. Accordingly, most of the heat energy reaching the open grill has traveled at least eight inches from the heating element assembly or from a reflective side panel. Because the reflective side panels lie at a mutually included angle of 90 degrees or more the reflected heat energy is dispersed across the open grill into the surrounding area. Hot spots are avoided because none of the heat energy is focused. The reflective side panels may be formed with vertical ribs for rigidity and also to create a pleasing visual effect due to the reflection from different planes of the visible light created by the heating element assembly.
Also forming part of the reflector assembly are horizontally extending, reflective top and bottom walls. Heat energy impinging on these walls and exiting from the open grill at the front of the reflector assembly is also dispersed across the open grill into the surrounding area. The horizonal top and bottom walls also avoid any focusing of the heat energy which might produce hot spots.
The reflector assembly may also include a reflective rear panel that connects the side panels and that is located behind the heating element assembly. Heat energy reflected by the rear panel is mostly reflected back to the heating element assembly or to the side panels. The reflective side panels and rear panel preferably are formed from a single piece of sheet metal, preferably tin plated steel. The reflective top and bottom walls can be separately formed from the same material.
Further in accordance with this invention, room air is drawn into the heater from below the reflector assembly and forced upwardly by a motorized fan through an air passage behind the reflector assembly and then through an open control chamber at the top of the heater before passing through ducts positioned along the top front edge of the reflector assembly. As well known, the air temperature at the floor of a room is cooler than the air above the floor and becomes increasingly warmer toward the ceiling of the room. Accordingly, air drawn into the bottom of the heater of this invention is relatively cool. This air is warmed as it rises inside the heater housing because it picks up heat from the backside of the reflective side and rear panels. A thermostatic control is positioned in the inside top portion of the heater. This location, as opposed to the bottom of the heater, is deemed better representative of the room air temperature sought to be obtained because of the warming of the relatively cool air drawn into the bottom of the heater. A thermostat located at the top of the heater tends to cycle on and off more frequently than would be the case if the thermostat were located upstream of the reflector assembly, near the bottom of the heater, but it enhances the ability of the thermostat to so control the heater as to maintain a relatively constant room temperature. In the preferred practice of this invention, baffles are provided to direct the air flow toward the thermostat. In addition, the power switch is also located at the top of the heater and control knobs for both the power switch and the thermostat extend upwardly from the top of the housing for ease of operation.
As a result of the combined effect of the cooling of the heater caused by the air flowing upwardly from the bottom of the heater and the sensitivity and responsiveness of the thermostatic control, a heater in accordance with this invention may have exterior housing parts which are relatively cool to the touch, thereby allowing selected exterior housing parts to be molded from thermoplastic materials which can readily be formed to aesthetically pleasing designs.
Yet another object of this invention is to provide an improved quartz heating element assembly for use in an electric heater and, more particularly, an improved heating element assembly which may be located above a fan blade. Such a heating element assembly in accordance with this invention comprises a pair of quartz heating elements each of which comprises a resistance heater wire inside a heat-radiating quartz tube. The tubes are closed at their ends by ceramic holders. Two cold wires or rods, one at each end of the resistance wire, are spot-welded to the resistance wire in each tube. The ends of the cold rods opposite the ends thereof welded to the resistance wire are connected, as by crimped connectors, to flexible wires that connect the heating elements into the heater control circuit. The cold wire at the bottom of each heating element extends horizontally outwardly in the space between the fan blade and the lower ceramic holder to a point sufficiently spaced in a horizontal direction from the center axis of the fan blade that the flexible wire can be safely connected thereto at that point.
Yet another object of this invention is to decrease the noise associated with the operation of quartz heaters. A quartz heating element typically produces an annoying noise each time it is energized. In accordance with this invention, the noise is substantially reduced by placing the resistance heater wire under slight tension by elongating it so that its coils are not simply stacked, in a relaxed condition, one on top of the other. The elongation is relatively quite small, on the order of ⅝ inch for a resistance heating wire having a coiled length of about 14 xc2xc inches, and does not appear to separate the coils from one another. An elongation which is adequate to substantially decrease the start-up noise can be determined by trial and error, but is preferably only so much as to reduce noise. A substantial elongation, such as would cause the wire coils to be noticeably spaced from one another, would likely adversely affect the useful life of the heating element. The reasons why such a relatively small elongation decreases the start-up noise is not fully known, but may be due to the lessening of the frictional engagement between the mutually adjacent coils which are caused to vibrate relative to one another due to magnetic effects which are present during start-up. The magnetic effects would presumably disappear as soon as the resistance wire heats to a temperature exceeding its Curie temperature.
To achieve their desired elongation, the coiled resistance wires are suspended from the upper ceramic holder by means of cooperating surfaces of the upper ceramic holder and the upper cold wires and, in addition, the resistance wires are stretched by the desired amount in order to bring surfaces of the lower cold wires into engagement with downwardly facing surfaces of the lower ceramic holder.
Other objects and advantages will become apparent from the following description and the accompanying drawings.